In some mail I received from Chris G. Demetriou, sie wrote
>
> > - 32-bit dev_t split up as {
> > 12 bits major
> > 20 bits minor {
> > 10 bits "unit"
> > 10 bits "subunit"
> > }
> > }
> > (interpretation of minor is left to the device itself; disks and
> > tapes use the subunit while ttys are generally just sequential);
> > ls -l shows <major,unit,subunit> (even on ttys).
>
> What is the definition of 'unit'? For example, take SCSI. Does
> device,LUN -> unit and partition number -> subunit, or does device ->
> unit and LUN fit into subunit (with other information, e.g. partition
> number)? Looking at the list Paul Vixie posted, it looks like the
> former.
Hmm, I was thinking about the scsi case and came up with this:
major = 12
minor = 20 :
- 4 bits bus
- 4 bits target
- 4 bits lun
- 4 bits slice
- 4 bits partition
To my thinking, device = (bus,target) and subunit = (lun,slice,partition)
I'm trying not to think about Fibre channel devices - from what people
have said about it being able to hold 1000+ devices, a 20 bit minor just
isn't big enough to hold all the information required.
That is, a "unit" is an attachment to the bus and "subunit" is a device
within that attachment.
Darren